//引用计数 reference count
const user1 = { age: 1 }
const user2 = { age: 2 }
const user3 = { age: 3 }
const nameList = [user1.age, user2.age, user3.age]

function fn() {
    const num1 = 1
    const num2 = 2 //当fn执行完，num1和num2的内存空间就会被回收掉
}
fn()